Study of the rare earth elements fractionation by solvent extraction:: Use of HPLC as an analytical control technique

The influence of the acidity and concentration of the rare earth elements (REE) in aqueous phase, the organic/aqueous phase ratio and the HCl concentration in stripping was estimated for the REE fractionation by solvent extraction. The assays were performed in batch tests by using 2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester, diluted in isododecane (1 mol l −1). The solution studied presented a REE concentration of 16.54 g l −1 (Nd 4.84%, Sm 61.36%, Eu 1.75%, and Gd 32.05%) in 0.77 mol l −1 hydrochloric medium. In order to control the analytical parameters (acidity and concentration of REE) in the aqueous solutions generated by the separation stages of the batch tests, a high-performance liquid chromatography (HPLC) technique was employed. The REE were separated from each other with α-hydroxyisobutyric acid as eluent and n-octane sodium sulphonate as modifying agent, in a C 18 reverse phase column. Eluted REE were monitored at 520 nm by a spectrophotometer after a post-column reaction with 4-(2-pyridylazo)resorcinol. Results are reported as extraction profiles and a chromatogram. For the studied parameters, it was found that, in lower acidity and concentration solutions, higher extraction percentages for the REE are obtained. In all assays, Gd and Eu were preferably extracted.